1. Field of the Invention
The present invention relates to thermosetting powder coating compositions and more particularly to powder coating compositions which have good exterior durability.
2. Brief Description of the Prior Art
Powder coating compositions for use in painting are extremely desirable. Such coating compositions greatly reduce and can even eliminate the organic solvents used in liquid paints. When the powder coating composition is cured by heating, little if any volatile material is given off to the surrounding environment. This is a significant advantage over liquid paints in which organic solvent is volatilized into the surrounding atmosphere when the paint is cured by heating.
For exterior durability, the powder coating composition is usually formulated with an acrylic polymer. The curing mechanism is also important and one of the better ones for attaining exterior durability is based on an acid group-containing acrylic polymer and triglycidyl isocyanurate (TGIC) curing agent. Although powder coating compositions using these materials give coatings with good exterior durability, they are expensive to formulate because of the TGIC and often have poor stability and give coatings which are often deficient in other physical properties.